1. Field of the Invention
This invention relates to a hot water circulating system, and more particularly to a hot water circulating system for, for example, space heating which is adapted to supply hot water heated by a burner to a radiator by means of steam pressure without using a circulation pump.
2. Description of the Prior Art
A hot water circulating system which is adapted to carry out circulation of hot water heated in a water boiler to a radiator by means of not a circulation pump but steam pressure is conventionally proposed, as disclosed in Japanese Utility Model Publication No. 53929/1982, disclosure of which is incorporated herein by reference.
Such a conventional hot water circulating system is constructed in such a manner that steam pressure generated from a water boiler heated by a burner causes hot water in the water boiler to be forcibly fed to a radiator and then through a circulating pipe connected between the radiator and an open tank arranged at a position above the water boiler to the open tank, and water stored in the open tank is returned through an on-off valve or check valve to the water boiler. A structure for returning water to the water boiler utilizes a solenoid valve as the check valve, and the solenoid valve is operated by a signal generated from a level detector.
Another conventional hot water circulating system is disclosed in Japanese Patent Application No. 97966/1980, of which disclosure is incorporated herein by reference. The system is so constructed that an open pipe is arranged to communicate a water boiler and an upper space in an open tank and provided with a pressure release valve which is actuated by a signal generated from a level detector. A circulating pipe for connecting a radiator to the open tank is communicated directly to the upper space of the open tank.
As described above, in each of the conventional hot water circulating systems described above, returning of water stored in the open tank to the water boiler is carried out utilizing a signal generated from the level detector. This causes the returning to start while a significant amount of hot water still remains in the water boiler, resulting in a ratio of the amount of hot water supplied to the radiator to a volume of the water boiler in each hot water circulating cycle being decreased. Also, the conventional system exhibits another disadvantage that steam pressure in the water boiler escapes to the open tank to cause much energy loss when water stored in the open tank is returned to the water boiler.
Further, in the conventional system, the circulating pipe is arranged between the radiator and the open tank so as to directly connect both and the open tank is required to serve also as a storage tank, so that heat loss is further increased. In view of this respect, the conventional system is adapted to use heat contained in exhaust gas for preheating water. Nevertheless, water cooled in the radiator is substantially heated in only the water boiler.
In addition, in the conventional system, an increase in a temperature of water returned to the open tank due to, for example, an increase in a temperature in a room in which the radiator is placed causes an increase in the amount of water evaporated from the open tank, so that replenishment of circulated water is frequently required.
Accordingly, it would be highly desirable to develop a hot water circulating system which is capable of increasing the amount of hot water to be circulated in each circulating cycle, decreasing energy loss and decreasing loss of water by evaporation.